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Unformatted text preview: FREQUENTLY ASKED QUESTIONS October 5, 2011 Administrative Questions When will homeworks be assigned? Ill post the first one by Friday. Content Questions How would I know if 1 , 1 , 1 ,... isnt just a coincidental but perfectly honest coin toss? Gut feelings about probability can be notoriously wrong. Indeed, you can never be absolutely sure that 20 tails in a row isnt an honest sequence. However in this case (and a lot of cases in real life) you can actually quantify how often this will happen, given a fair coin with equal probability of heads or tails. The probability is given by the binomial distribution: its P (20) = 20! 20!0! . 5 20 . 5 = 9 . 5 10- 7 . How improbable does a coin toss sequence have to be before you decide the coin is loaded? Well, that may be up to your gut feeling and your threshold may depend on the situation. . but you can still make the quantitative statement. (Personally, if someone wanted to play a game of coin-flipping for money and this happened the first time, Id be a little worried. ..) Why is rand() so bad? Typically system-provided rand functions use very poor quality linear con- gruential generators they will have short periods and/or correlations be- tween numbers. In general, if you are using random numbers for anythingtween numbers....
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- Fall '11